2. Stephen and Hugh take a walk in a national park. They measure their elevation in metres above sea level before they start, and every hour throughout their walk, as shown in the graph below. OA +7(m) (257) (0,49 (0149) (1,44) (3,50) (hours) Their elevation after hours can be modelled by the function y = at3 + bt + ct + d for 0 t3. (a) State the value of d. [1 mark] (b) Using a GDC, find the values of a, b, and c. [3 marks] (c) Estimate their elevation after 2 hours. [2 marks] (d) Their actual elevation after 2 hours is 60 m. Calculate the percentage error in part (c). [2 marks]